Methodological issues in coding sleep states in immature infants

Precision caffeine therapy for apnea of prematurity and circadian rhythms: New possibilities open up

Caffeine is the globally consumed psychoactive substance and the drug of choice for the treatment of apnea of prematurity (AOP), but its therapeutic effects are highly variable among preterm infants. Many of the molecular underpinnings of the marked individual response have remained elusive yet. Interestingly, the significant association between Clock gene polymorphisms and the response to caffeine therapy offers an opportunity to advance our understanding of potential mechanistic pathways. In this review, we delineate the functions and mechanisms of human circadian rhythms. An up-to-date advance of the formation and ontogeny of human circadian rhythms during the perinatal period are concisely discussed. Specially, we summarize and discuss the characteristics of circadian rhythms in preterm infants. Second, we discuss the role of caffeine consumption on the circadian rhythms in animal models and human, especially in neonates and preterm infants. Finally, we postulate how circadian-based therapeutic initiatives could open new possibilities to promote precision caffeine therapy for the AOP management in preterm infants.

Early development of sleep and brain functional connectivity in term-born and preterm infants

The proper development of sleep and sleep-wake rhythms during early neonatal life is crucial to lifelong neurological well-being. Recent data suggests that infants who have poor quality sleep demonstrate a risk for impaired neurocognitive outcomes. Sleep ontogenesis is a complex process, whereby alternations between rudimentary brain states-active vs. wake and active sleep vs. quiet sleep-mature during the last trimester of pregnancy. If the infant is born preterm, much of this process occurs in the neonatal intensive care unit, where environmental conditions might interfere with sleep. Functional brain connectivity (FC), which reflects the brain's ability to process and integrate information, may become impaired, with ensuing risks of compromised neurodevelopment. However, the specific mechanisms linking sleep ontogenesis to the emergence of FC are poorly understood and have received little investigation, mainly due to the challenges of studying causal links between developmental phenomena and assessing FC in newborn infants. Recent advancements in infant neuromonitoring and neuroimaging strategies will allow for the design of interventions to improve infant sleep quality and quantity. This review discusses how sleep and FC develop in early life, the dynamic relationship between sleep, preterm birth, and FC, and the challenges associated with understanding these processes. IMPACT: Sleep in early life is essential for proper functional brain development, which is essential for the brain to integrate and process information. This process may be impaired in infants born preterm. The connection between preterm birth, early development of brain functional connectivity, and sleep is poorly understood. This review discusses how sleep and brain functional connectivity develop in early life, how these processes might become impaired, and the challenges associated with understanding these processes. Potential solutions to these challenges are presented to provide direction for future research.

The interaction between diet and neurobehavior in very low birth weight infants

BACKGROUND

Modulation of behavior and physiology by dietary perturbations early in life can provide clues to the pathogenesis of adult diseases. We tested the hypothesis that a period of early protein supplementation modulates sympathetic nervous system activity demonstrated indirectly by an increase in active sleep state distribution in very low birth weight (VLBW) infants.

METHODS

VLBW infants (n = 71) were randomized to a total parenteral nutritional regimen providing 18% of the energy intake as amino acids (AA) or a conventional regimen providing 12.5% to achieve targeted AA intakes of 4 g/kg/day (0.004 kcal/kg/day) and 3 g/kg/day (0.003 kcal/kg/day), respectively. Both groups were weaned to enteral feeding and advanced to provide similar AA intake of 4 g/kg/day (0.004 kcal/kg/day). Six-hour daytime, behavioral sleep studies were performed when the infants reached full enteral intake (165 ml/kg/day).

RESULTS

Infants in the high protein group spent more time in active sleep (77.2 ± 10.5% vs. 70.7 ± 11.8%), p < 0.01 and less time in quiet sleep (12.9 ± 3.4% vs. 17.7 ± 7.0%, p < 0.01) as compared to the conventional group. No group differences were observed for indeterminate sleep, awake, or crying states.

CONCLUSIONS

These results suggest that dietary intake may indirectly influence sympathetic nervous system activity.

IMPACT

Infants randomized to an early, high protein nutritional regimen spent an increased percentage of time in active sleep, supporting the hypothesis that nutrition and behavior are interactive. Furthermore, sleep states are an indirect measure of sympathetic nervous system activity, suggesting that dietary intake may influence sympathetic nervous system activity. This study highlights the importance of considering the impact of nutrition during critical periods of development in order to further understand and improve the long-term outcomes of very low birth weight infants.

Sleep-Wake States and Feeding Progression in Preterm Infants

BACKGROUND

Previous studies demonstrated a short-term relationship between infant sleep-wake states and oral feeding performance, with state being an indication of infants' neurobehavioral readiness for feeding. However, the relationship between sleep-wake states and feeding skills has not been evaluated longitudinally during hospitalization.

OBJECTIVES

The purpose of this study was to examine preterm infants' sleep-wake state developmental trajectories and their associations with feeding progression during hospitalization.

METHODS

This descriptive and exploratory study was a secondary analysis using data from a longitudinal two-group, randomized controlled trial evaluating the effects of early and late cycled light on health and developmental outcomes among extremely preterm infants who were born ≤28 weeks of gestational age. Sleep-wake states were assessed for two 2-hour interfeeding periods per day (day and night hours), 30 weeks postmenstrual age, and every 3 weeks until discharge. Occurrences of active sleep, quiet sleep, and waking were recorded every 10 seconds. Feeding progression was assessed based on an infant's postmenstrual age at five milestones: first enteral feeding, full enteral feeding, first oral feeding, half oral feeding, and full oral feeding. Trajectory analyses were used to describe developmental changes in sleep-wake states, feeding progression patterns, and associations between feeding progression and sleep-wake trajectories.

RESULTS

Active sleep decreased while waking, and quiet sleep increased during hospitalization. Two distinct feeding groups were identified: typical and delayed feeding progression. In infants with delayed feeding progression, rates of active and quiet sleep development during the day were delayed compared to those with typical feeding progression. We also found that infants with delayed feeding progression were more likely to be awake more often during the night compared to infants with typical feeding progression.

DISCUSSIONS

Findings suggest that delays in sleep-wake state development may be associated with delays in feeding progression during hospitalization. Infants with delayed feeding skill development may require more environmental protection to further support their sleep development.

Perinatal antibiotics alter preterm infant EEG and neurobehavior in the Family Nurture Intervention trial

Early exposure to antibiotics has been shown to increase risk for poor neurobehavioral development, particularly with regard to attention deficit disorders. Clinically, electroencephalography (EEG) is increasingly used as a biomarker of these deficits. Less is known about the effects of antibiotics on neurobehavioral and neurophysiological outcomes in preterm infants, a population at particularly high risk for attention deficits and perinatal antibiotic exposure. This study examines the effects of perinatal antibiotic exposure on neonatal EEG and attention deficits as measured by the Child Behavior Checklist in 4- to 5-year-old children who were enrolled in an NICU-based randomized controlled trial comparing Family Nurture Intervention (FNI) to standard care. Antibiotic-exposed infants had increased attention problems and there was a main effect of antibiotic exposure such that exposed infants had higher EEG power. This effect was fourfold greater in infants who received standard NICU care compared to those who received the intervention, suggesting a buffering effect of the intervention. We hypothesize that the relationship between antibiotic exposure and altered neurodevelopment may be due to effects of antibiotics on the microbiome, and that FNI may buffer these adverse consequences.

Does preterm period sleep development predict early childhood growth trajectories?

OBJECTIVE

The current study examined the relationship between sleep state development across the preterm and early post-term periods and subsequent growth trajectories from 1 to 27 months corrected age.

STUDY DESIGN

Retrospective analysis of data collected prospectively from 111 preterm infants (⩽34 weeks gestation) who participated in a multi-site longitudinal study. Separate longitudinal parallel process models were calculated for each sleep state (active and quiet sleep) and growth (weight, length and body mass index (BMI) Z-scores) variable to estimate the associations between their developmental trajectories.

RESULTS

Significant associations were identified between the trajectories of quiet sleep and weight, active sleep and weight, quiet sleep and BMI, and active sleep and BMI. No statistically meaningful associations were identified between the trajectories of early childhood length and the preterm sleep states.

CONCLUSION

Faster preterm period sleep development appears to predict more favorable early childhood growth trajectories, particularly for weight, indicating preterm sleep may be an important biomarker for subsequent growth outcomes.

An automated method for coding sleep states in human infants based on respiratory rate variability

A novel quantitative method for coding epochs of active and quiet sleep in infants using respiration is reported. The approach uses the variance of the instantaneous breathing rate within brief epochs of sleep. Variances are normalized within subject by dividing by the 75th percentile variance across epochs. Then, a normalized variance active sleep threshold of 0.29 was determined to produce the highest concordance with a method based on visual inspection of respiratory variability (100% and 90% for quiet and active sleep, respectively). The method was independently validated by comparing to standard polysomnographic state coding (87% and 80% concordance for quiet and active sleep) as well as with behavioral state coding (92% and 78% for quiet and active sleep). Validity was also demonstrated by showing that sleep states identified by the method resulted in the expected state differences in infant heart rate variability and electrocortical activity.

Behavioral observation differentiates the effects of an intervention to promote sleep in premature infants: a pilot study

PURPOSE

Sleep and ongoing cycling of sleep states are required for neurosensory processing, learning, and brain plasticity. Many aspects of neonatal intensive care environments such as handling for routine and invasive procedures, bright lighting, and noise can create stress, disrupt behavior, and interfere with sleep in prematurely born infants. The study empirically investigated whether a 30-minute observation of infant sleep states and behavior could differentiate an intervention to promote sleep in premature infants with feeding difficulties relative to conventional care (standard positioning, standard crib mattress [SP]). We included an intervention to determine the ability of the method to discriminate treatments and generate a benchmark for future improvements. The intervention, a conformational positioner (CP), is contoured around the infant to provide customized containment and boundaries. To more fully verify the 30-minute observational sleep results, standard polysomnography was conducted simultaneously and sleep outcomes for the 2 modalities were compared.

SUBJECTS

In a randomized crossover clinical trial, 25 infants, 31.5 ± 0.6 weeks' gestational age and 38.4 ± 0.6 weeks at the study, with gastrointestinal conditions or general feeding difficulties used each intervention during an overnight neonatal intensive care unit sleep study.

METHODS

Infant sleep states and behaviors were observed during two 30-minute periods--that is, on the positioner and mattress--using the naturalistic observation of newborn behavior. Two certified developmental care nurses assessed sleep state, self-regulatory, and stress behaviors during 2-minute intervals and summed over 30 minutes. Sleep characteristics from standard polysomnography were measured at the time of behavior observations.

RESULTS

Infants on CP spent significantly less time in alert, active awake, or crying states by observation compared with SP. Surgical subjects spent more time awake, active awake, or crying and displayed a higher number of behavior state changes than the nonsurgical infants. The percentage of time in observed deep sleep and quiet sleep was correlated with both percentage sleep efficiency (r = 0.78) and fewer state shifts per hour (r = -0.65) from electroencephalogram (EEG). Sleep efficiency by EEG was greater on CP versus SP.

CONCLUSIONS

The CP enabled sleep compared with the standard mattress (SP) over 30-minute observation periods. Sleep status from behavioral observation was verified by standard EEG-based sleep techniques. Behavioral observation of sleep states may be a useful strategy for measuring the effectiveness of strategies to facilitate sleep in premature infants. Surgical subjects may benefit from additional interventions to promote sleep.

Conformational positioning improves sleep in premature infants with feeding difficulties

OBJECTIVE

To determine whether premature infants' sleep organization, total sleep time, and arousals may be modulated while on a conformational positioner that provides boundaries, customized positioning, and containment compared with standard positioning (standard crib mattress).

STUDY DESIGN

A proof of concept trial using a within subject crossover design was conducted among 25 premature infants with feeding difficulties. Infants of 31.5 weeks gestational age served as their own control during overnight polysomnography at postconceptual age 38.4 weeks. Each baby received both interventions (order randomized), 1 for each one-half of the 10.5-hour study.

RESULTS

Use of the conformational positioner resulted in higher sleep efficiency of 61% vs 54% for the standard mattress (P < .05). The interventions did not differ for percent active sleep, percent quiet sleep, percent indeterminate sleep, or spontaneous arousals. Sleep efficiency was higher on the conformational positioner than standard positioning for surgical subjects and for subjects with necrotizing enterocolitis or gastroschisis (n = 10). The surgical subjects (n = 9) had lower sleep efficiency, lower percentage of active sleep, and more spontaneous arousals compared with the nonsurgical group.

CONCLUSIONS

The use of the conformational positioner improved sleep efficiency vs the standard mattress in premature infants with feeding difficulties. Infants requiring surgery or with gastrointestinal diagnoses may be more susceptible to environmental stress.

Electroencephalographic activity of preterm infants is increased by Family Nurture Intervention: a randomized controlled trial in the NICU

OBJECTIVE

To assess the impact of Family Nurture Intervention (FNI) on electroencephalogram (EEG) activity in preterm infants (26-34 weeks gestation).

METHODS

Two groups were tested in a single, level IV neonatal intensive care unit (NICU; standard care or standard care plus FNI) using a randomized controlled trial design. The intervention consists of sessions designed to achieve mutual calm and promote communication of affect between infants and their mothers throughout the NICU stay. EEG recordings were obtained from 134 infants during sleep at ∼35 and ∼40 weeks postmenstrual age (PMA). Regional brain activity (power) was computed for 10 frequency bands between 1 and 48 Hz in each of 125 electrodes.

RESULTS

Near to term age, compared to standard care infants, FNI infants showed robust increases in EEG power in the frontal polar region at frequencies 10 to 48 Hz (20% to 36% with p-values <0.0004). Effects were significant in both quiet and active sleep, regardless of gender, singleton-twin status, gestational age (26-30 or 30-35 weeks) or birth weight (<1500 or >1500 g).

CONCLUSION

FNI leads to increased frontal brain activity during sleep, which other investigators find predictive of better neurobehavioral outcomes.

SIGNIFICANCE

FNI may be a practicable means of improving outcomes in preterm infants.

Effects of body position on thermal, cardiorespiratory and metabolic activity in low birth weight infants

BACKGROUND

Low birth weight (LBW) infants sleeping prone are known to exhibit many physiological differences from those sleeping supine, including lower energy expenditure (heat production) and higher surface temperature. This apparent increase in heat storage suggests that heat loss may be inhibited in the prone position which, in turn, might influence cardiorespiratory activity.

AIMS

To determine the effects of body position (prone vs. supine) on absolute surface temperature profile (heat storage), central-peripheral (C-P) thermal gradients (vasomotor response), cardiorespiratory activity and metabolic gas exchange in growing LBW infants.

METHODS

Six-hour continuous recordings of absolute surface temperature profiles, cardiorespiratory activity and O2 and CO2 exchange, along with minute-to-minute assessment of behavioral sleep states were performed in 32 healthy growing LBW infants (birth weight 805-1590 g, gestational age 26-35 weeks and postconceptional age at study 33-38 weeks). Each infant was randomly assigned to the prone or supine position for the first 3 h of the study and then reversed for the second 3 h. Surface temperatures were recorded from 4 sites (forehead, flank, forearm and leg) and averaged each minute. Central (forehead and flank)-to-peripheral (forearm and leg) and forehead-to-environment (H-E) thermal gradients were calculated from the surface temperatures. Corresponding sleep states were aligned with minute averages obtained from the temperature and cardiorespiratory measurements. Data were then sorted for prone and supine positions during quiet (QS) and active sleep (AS) and compared using paired t-tests.

RESULTS

In the prone position during both AS and QS, infants had higher forehead, flank, forearm and leg surface temperatures, narrower C-P gradients, higher heart rates and respiratory frequency, and lower heart rate and respiratory variability. Despite similar environmental temperatures, the H-E gradient was higher in the prone position. In the prone position infants demonstrated lower O2 consumption and CO2 production and a higher respiratory quotient.

CONCLUSIONS

Despite thermoregulatory adjustments in cardiorespiratory function, infants sleeping prone have relatively higher body temperature. The cardiorespiratory responses to this modest increase in temperature indicate that thermal and metabolic control of cardiac and respiratory pumps seem to work in opposition. The consequences of any attendant changes in blood gas activity (e.g. hypocapnia and/or increased mixed venous oxygen concentration) due to this override of metabolic control remains speculative.

EEG functional connectivity in term age extremely low birth weight infants

OBJECTIVE

The hypothesis is tested that electrocortical functional connectivity (quantified by coherence) of extremely low birth weight (ELBW) infants, measured at term post-menstrual age, has regional differences from that of full term infants.

METHODS

128 lead EEG data were collected during sleep from 8 ELBW infants with normal head ultrasound exams and 8 typically developing full term infants. Regional spectral power and coherence were calculated.

RESULTS

No significant regional differences in EEG power were found between infant groups. However, compared to term infants, ELBW infants had significantly reduced interhemispheric coherence (in frontal polar and parietal regions) and intrahemispheric coherence (between frontal polar and parieto-occipital regions) in the 1-12Hz band but increased interhemispheric coherence between occipital regions in the 24-50Hz band.

CONCLUSIONS

ELBW infants at term post-menstrual age manifest regional differences in EEG functional connectivity as compared to term infants.

SIGNIFICANCE

Distinctive spatial patterns of electrocortical synchrony are found in ELBW infants. These regional patterns may presage regional alterations in the structure of the cortex.

Apneic preterms and methylxanthines: arousal deficits, sleep fragmentation and suppressed spontaneous movements

OBJECTIVE

To determine if apneic preterm infants currently treated with methylxanthines develop evidence of sleep deprivation from cumulative arousal and motor activational effects.

STUDY DESIGN

Sleep, wake, arousal and actigraphic movements were monitored in extubated clinically stable premature infants (N=37). Neonates were free of other medications for >72 h and were grouped based on methylxanthine exposure: >5 days with caffeine (n=14), >5 days theophylline (n=13) or no prior exposure (n=10).

RESULT

Duration of methylxanthine treatment predicted increased arousals, wakefulness and actigraphic movements, and decreased active sleep. Recording from 1200 to 0500 hours, methylxanthine-treated groups showed reductions in all arousal parameters: waking state, number of wake epochs, brief arousals and composite arousal index, and shorter fast-burst, sleep-related motility than untreated controls.

CONCLUSION

In apneic preterms, chronic methylxanthine treatment appears to produce sleep deprivation secondary to the stimulatory action of methylxanthines on arousal and motor systems.

Sleep in the neonatal intensive care unit

Recent experimental data suggest a strong role for sleep in brain development. As sleep is the predominant behavioral state in the term and especially the preterm newborn, these data underline the importance of respecting sleep duration and organization within the different sleep states. Polysomnography is the preferred technique used for identification of sleep state; however, behavioral observations-under the condition that the observer is well trained-may prove as efficient. Newborns hospitalized in the neonatal intensive care unit are exposed to many stimuli and care activities that disrupt their sleep organization and may have irreversible effects on their brain development. In order to improve the long-term neurobehavioral outcome of these high-risk subjects, a consistent care approach is proposed. Application of the Neonatal Individualized Developmental Care and Assessment Program decreases environmental stressful events and promotes harmonious well-being behaviors, based on an individual approach. This strategy has encouraging results, showing an increase in sleep duration under Neonatal Individualized Developmental Care and Assessment Program conditions, but further studies are needed to assess its long-term neurobehavioral impact.

Sleeping position and electrocortical activity in low birthweight infants

OBJECTIVE

To evaluate the effects of prone and supine sleeping positions on electrocortical activity during active (AS) and quiet (QS) sleep in low birthweight infants.

DESIGN

Randomised/crossover study.

SETTING

Infant Physiology Laboratory at Children's Hospital of New York.

PATIENTS

Sixty three healthy, growing, low birthweight (birth weight 795-1600 g) infants, 26-37 weeks gestational age.

INTERVENTIONS

Six hour continuous two channel electrocortical recordings, together with minute by minute behavioural state assignment, were performed. The infants were randomly assigned to prone or supine position during the first three hours, and positions were reversed during the second three hours.

OUTCOME MEASURES AND RESULTS

Fast Fourier transforms of electroencephalograms (EEGs) were performed each minute and the total EEG power (TP), spectral edge frequency (SEF), absolute (AP) and relative (RP) powers in five frequency bands (0.01-1.0 Hz, 1-4 Hz, 4-8 Hz, 8-12 Hz, 12-24 Hz) were computed. Mean values for TP, SEF, AP, and RP in the five frequency bands in the prone and supine positions during AS and QS were then compared. In the prone sleeping position, during AS, infants showed significantly lower TP, decreased AP in frequency bands 0.01-1.0 Hz, 4-8 Hz, 8-12 Hz, 12-24 Hz, increased RP in 1-4 Hz, and a decrease in SEF. Similar trends were observed during QS, although they did not reach statistical significance.

CONCLUSIONS

The prone sleeping position promotes a shift in EEG activity towards slower frequencies. These changes in electrocortical activity may be related to mechanisms associated with decreased arousal in the prone position and, in turn, increased risk of sudden infant death syndrome.

Distribution of sleep and wakefulness EEG patterns in 24-h recordings of preterm and full-term newborns

The aim of this study was to evaluate the organisation of EEG patterns in 24-h recordings of preterm and near-term neonates. In particular, the distribution of the different EEG codes at different postmenstrual ages (PMA) and the variations of sleep-related EEG pattern organisation was studied, during day (8.00 a.m.-8.00 p.m.) and night (8.00 p.m.-8.00 a.m.) time. The age of appearance of different neonatal EEG patterns, previously described in literature for short lasting records, was confirmed in this 24-h study. The medium-voltage continuous EEG pattern (pattern "3") was less represented approaching term age, in coincidence with the appearance of the two low-voltage continuous patterns ("1" and "2"), which are also related to active sleep and wakefulness. Discontinuous pattern ("7") was also less represented with age, but in day-time only. The percentage of time occupied by this pattern, related to quiet sleep, was significantly higher during day-time hours, than at night.

Sleeping and waking state development in preterm infants

BACKGROUND

Most studies of sleep-wake states of preterm infants have been cross-sectional. Thus, the extent to which sleep-wake development occurs within individuals and how environmental factors affect the development of sleeping and waking is unclear.

AIMS

This study examined the development of sleeping and waking during the preterm and early post-term periods and the effects of infant health and environmental characteristics.

DESIGN

Longitudinal, descriptive design.

PARTICIPANTS

134 preterm infants at high risk for developmental problems because of birthweights under 1500 g or mechanical ventilation.

OUTCOME MEASURES

Weekly 2-h behavioral observations were conducted from the time infants were no longer critically ill until 43 weeks post-conceptional age or discharge. A single follow-up observation was conducted 1-3 months later.

RESULTS

Active sleep, large body movements and the percent of no REM during active sleep decreased with age, and quiet waking, active waking, quiet sleep and regularity of respiration in active sleep and quiet sleep increased. The state of sleep-wake transition increased until 40 weeks and then decreased after 43 weeks CA. Negative facial expressions showed a quadratic decrease over age. Active waking, active sleep, negative facial expressions and quiet sleep regularity showed a change of development after term. Infant characteristics, illness severity and medical treatments, the handling due to performing an EEG and hospital had only minor effects.

CONCLUSIONS

Significant development of sleeping and waking occurs over the preterm period. Additional research is needed to determine how the change from the hospital to the home environment affects on these developmental trajectories.

EEG patterns in 10 extreme premature neonates with normal neurological outcome: qualitative and quantitative data

The aim of this prospective study was to describe and quantify EEG patterns in 10 very premature infants (24 weeks 2 days- 26 weeks 4 days GA) without neonatal neurological pathology and with a normal outcome at 3 years of age for nine of them. EEG and eye movements were recorded in the first 5 days of life. All tracings were discontinuous; EEG inactivity (<15 microV) never exceeded 1 min, representing 45.3% of total recording time. The EEG bursts, mainly synchronous, could last up to 83 s when >50 microV and to 197 s when >15 microV. High voltage delta waves (0.5 Hz; up to 330 microV), either smooth or superimposed with 7-12 Hz rhythms, were the most typical and frequent figures, mainly in temporal (mean number 257.2 +/- 73.3) and occipital (237.7 +/- 65.8 per hour recording) areas. In temporal areas, they appeared mainly in clusters; more often unilateral than bilateral (P < 0.05). Occipital delta waves were as often bilateral and synchronous as unilateral. The two distinct frontal delta waves were significantly less numerous than other delta waves (P < 0.05). Bursts of hypersynchronous high voltage delta waves and of diffuse sharp theta waves were less numerous than other waves (P < 0.01). Considering periods with or without eye movements, the mean percentage and the mean longest period of EEG activity (< or =50 microV) were significantly greater (P < 0.01) when eye movements were present, indicating a rough sleep state differentiation as early as 25 weeks CA. These EEG patterns are qualitatively and quantitatively reproducible. They constitute standards of normality and a basis for the determination of neurological prognosis.

Early steps of awakening process

This paper summarizes the main aspects of sleep and waking development and shows results about awakening as a function of age. Awakenings come mainly from active sleep and their number decreases with age. Understanding the awakening process should take into account the development of sleep and waking states and of circadian rhythms and homeostatic processes.

Nursing care and the development of sleeping and waking behaviors in preterm infants

The relationship between nursing care and the development of sleep-wake behaviors of 71 medically high-risk preterms was examined. The development of preterm infants' sleep-wake states, jitteriness, and negative facial expressions were influenced not only by the presence of the nurse, but also by the type of caregiving the nurse provided. The infant was awake more often when with caregivers than when alone. Waking states increased over time only when the infant was with caregivers, whereas quiet sleep increased only when the infant was alone. Infant behaviors and sleep-wake development were related to the intrusiveness of care. For example, negative facial expressions and sleep-wake transitions increased over time during the most intrusive caregiving. The development of sleeping and waking in preterm infants appears to depend not only on biological maturation but also nursing stimulation. As long-term developmental effects of nurse caregiving are unknown, additional research is needed.

The effect of sleep state on electroretinographic (ERG) activity during early human development

To assess the effects of sleep state on human retinal electric responses, full-field electroretinograms were obtained in a cross-sectional study from 123 preterm infants at 36, 40 and 56 weeks of post-gestational age. At each age, electroretinographic recordings were assigned to one of two groups according to whether the infants were in active sleep or quiet sleep. Both sleep states were determined behaviorally. Pure rod, maximal, 30 Hz flicker and light adapted single cone responses were evaluated when a sleep state was clearly established. Peak-to-peak amplitudes of most electroretinographic responses were significantly larger in active sleep relative to quiet sleep at 36 and 40 weeks of post-gestational age. We speculate that larger amplitudes during active sleep may play a role in the maturation of the visual system.

Body position, sleep states, and cardiorespiratory activity in developing low birth weight infants

The objective of this study was to determine the effects of body position (supine vs prone) on cardiorespiratory activity during quiet and active sleep in growing low birth weight (LBW) infants. The effect of postconceptional age on cardiorespiratory activity in the two positions was also evaluated. Fifty-one healthy, growing, appropriate for gestational age LBW infants (795-1600 g), ranging from 26-37 weeks in gestational age, were evaluated. All subjects were enrolled in an ongoing study of the effects of quality of dietary energy on the rate and composition of weight gain. Infants were randomly assigned to the supine or prone position for the first 3 h of the 6-h studies; the position was reversed for the second 3 h. Continuous recordings of cardiorespiratory activity were performed along with simultaneous minute by minute assignment of behavioral sleep state. Measurements of heart rate (HR), heart period variability (RR-SD), respiratory rate (f), and respiratory variability (fSD) were made each minute. Low birth weight infants had higher HR and f and lower RR-SD and fSD in the prone position compared to the supine position, during both quiet and active sleep. With increasing postconceptional age, positional differences in HR increased during quiet sleep and differences in RR-SD increased during both sleep states. These data demonstrate systematic differences in cardiorespiratory control related to body position during sleep. We speculate that such positional differences are due to variations in autonomic control, and may, in turn, contribute to variations in susceptibility to sudden infant death syndrome.

Temporal organization of sleep-wake states in preterm infants

The development of temporal organization of sleep-wake states during the preterm period was examined. Seventy-one high-risk preterms from two cohorts were observed from 7 to 11 p.m. weekly from the time they were no longer critical until discharge. Mixed general linear model analyses found that with increasing postconceptional age, quiet waking, active waking, and sleep-wake transition bouts occurred more frequently, quiet sleep bouts occurred less frequently, and active waking and quiet sleep bouts increased in length. However, these developmental patterns were not stable over cohorts. On the other hand, the transitional probabilities between states were similar in both cohorts, providing evidence for biological bases for some aspects of temporal organization. Active sleep was pivotal in state transitions. Younger infants showed fewer transitions that did not involve active sleep. Thus, temporal organization is an early characteristic of sleep-wake states but is not a unitary phenomenon. Transitional probabilities remain relatively invariant, whereas bouts lengths and frequencies may be altered in different populations or by differing environmental conditions.

Modeling development of sleep-wake behaviors: I. Using the mixed general linear model

The purpose of this paper is to demonstrate the use of the mixed general linear model (MixMod) for modeling development of sleep-wake behaviors in preterm infants. The mixed general linear model allows the concurrent identification of both group and individual developmental patterns in longitudinal data sets with inconsistently timed data, irregularly timed data, and randomly missing values. This statistical technique is well suited to data from preterm infants because these infants enter and leave longitudinal studies at varying times depending on their health status. One sleep organizational variable--the regularity of respiration in quiet sleep--obtained from a study of 37 preterm infants was used as an example. Seven infant characteristics were used as covariates. The various steps involved in conducting a mixed model analysis of this variable are illustrated. The strengths and limitations of this technique are discussed.

Modeling development of sleep-wake behaviors. II. Results of two cohorts of preterms

A mixed general linear model analysis of the development of sleep-wake states was conducted on 37 high-risk preterm infants and replicated with a second cohort of 34 infants. Most dependent variables showed significant development over the preterm period: active sleep decreased, and active waking, quiet waking, and the organization of active sleep and quiet sleep increased over the preterm period in both cohorts. The amount of quiet sleep also increased over age, but this change was significant only for Cohort 1. Seven infant characteristics used as covariates had only minor effects. There were no significant differences in the developmental trajectories (slopes) of the two cohorts. The amounts of four variables differed between cohorts: Cohort 2 infants had less sleep-wake transition, more active sleep, less active sleep without REM, and more regular quiet sleep. These findings suggest that developmental patterns of sleep wake states are stable enough in the preterm period that deviant individual patterns might be used to identify infants with neurological problems.

Rhesus macaques with high CSF 5-HIAA concentrations exhibit early sleep onset

The relationship between central nervous system serotonergic activity, as reflected by cerebrospinal fluid (CSF) concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), and sleep/wakefulness behavior was investigated in socially housed, juvenile rhesus macaques. Two cohorts of rhesus monkeys (Macaca mulatta), numbering 42 subjects (seventeen 39-month-olds and twenty-five 20-month-olds) were observed in their home cages between 21.30 h and 23.30 h for 10 nights using an infrared night scope. Over each 90-min observation period, the following states were recorded every 5 min using a scan sampling procedure: Sleep, Drowsy, Passive-awake and Active. After more than one quarter of the animals in the group had fallen asleep, states were recorded as they occurred. Six weeks prior to the collection of the behavioral data, a sample of cisternal CSF was obtained to assay for 5-HIAA concentrations. With cohort effects statistically controlled, there was a negative correlation between latency to fall asleep and CSF 5-HIAA concentrations (i.e., subjects with high CSF 5-HIAA concentrations were more likely to fall asleep early). Subjects with low CSF 5-HIAA concentrations were also more active during the daytime hours. Subjects who fell asleep first were, on average, also less active during nighttime hours. The positive correlation between CSF 5-HIAA and sleep onset was not a result of social status since there was no correlation between social dominance rank and time of sleep onset. These results support the hypothesis that the serotonergic system may play a role in sleep onset and possibly in the regulation of diurnal activity rhythms in non-human primates.

A novel quantitative measure of Tracé-alternant EEG activity and its association with sleep states of preterm infants

This study describes the application of a novel quantitative method for classifying patterns of EEG activity that are associated with the predominant sleep-states of newborn infants. Periods in which there are bursts of high-voltage slow wave activity in the EEG that alternate with periods of low-voltage activity are termed Tracé-alternant. During active or REM sleep. Tracé-alternant is absent and EEG activity is characterized by a variable mixture of frequencies including intermittent high frequency (10-20 Hz) activity superimposed on slower frequencies. Results show that an analytic method previously developed in fetal baboons for identifying EEG segments with and without Tracé-alternant successfully distinguishes homologous patterns of EEG activity in preterm infants. This method provides an excellent objective approach for monitoring changes in EEG patterns that are coincident with behaviorally defined sleep states.